Polymeric nets or webs are sheet-like fenestrate structures comprising polymeric material. Polymeric nets find utility in a variety of disparate applications ranging from electronics to medical care, and such nets are thus commercially important materials. These nets can have different qualities depending upon their mode of engineering. For example, such nets can be fashioned from a variety of polymers, have a variety of hole sizes and shapes, and can assume almost any desired thickness.
In many applications, it is desirable to have nets fashioned from relatively inert matter in order to avoid compromising the integrity of the net lattice or affecting materials in contact with the net. Polymers represent attractive choices for nets to be employed in these applications, as many polymers are extremely resistant to most chemicals. In fact, fluoropolymers such as polytetrafluoroethylene (PTFE) rank as some of the most chemically inert materials. Thus, nets of fluoropolymers would be highly useful in applications in which the nets are exposed to harsh conditions, such as in batteries, filtration apparatuses, and the like.
In other applications, it is desirable to fashion nets to include a minimal amount of extractable material, as such matter can affect the physical and chemical properties of the polymeric lattice, and hence the net, as well as contaminate materials in contact with the net. Nets comprising reactive extractable material are changed or degraded over time as the extractable material is removed from the net. Perhaps more importantly, in other applications, such as filtration devices in which nets are employed as filter media or as support elements, the presence of extractable matter in the net lattice adversely affects the ultimate quality of the filtrate. Notably, extractable matter can be leached from the net lattice, thus contaminating the filtrate and/or filtered material.
It is also often desirable to have extremely thin polymeric nets and nets with very small, regularly shaped holes or pores. Such nets are useful in filtration devices, especially ultrafiltration devices, for removing very small particles (e.g., microbes) from a fluid. Furthermore, very thin nets minimize the pressure differential across a filter during filtration, thus enhancing the efficiency of some types of filtration (e.g., dynamic or crossflow filtration).
Typically, many types of polymeric nets are manufactured by extrusion, by weaving, by knitting, or by punching holes or slits into a sheet of polymeric material. It is very difficult and costly to control the size and shape of holes or pores in nets produced by many of these processes, especially where very small and uniform holes are required and for very thin nets. Moreover, many commonly employed processes for fabricating nets, especially extrusion, are prone to introduce a significant amount of extractable matter (e.g., metals, resins, etc.) into the polymer lattice.
Thus, there exists a need for a net substantially free of extractable matter and a very thin net having substantially uniform hole size and shape. The present invention provides such a polymeric net, as well as a method of preparing same. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.